Automated data storage libraries are known for providing cost effective storage and retrieval of large quantities of data. The data in automated data storage libraries is stored on data storage media that are, in turn, stored on storage cells, shelves or the like inside the library in a fashion that renders the media, and its resident data, accessible for physical retrieval. Such media is commonly termed “removable media”. Data storage media may comprise any type of media on which data may be stored and which may serve as removable media, including but not limited to magnetic media (such as magnetic tape or disks), optical media (such as optical tape or disks), electronic media (such as PROM, EEPROM, flash PROM, Compactflash™, Smartmedia™, Memory Stick™, etc.), or other suitable media. Typically, the data stored in automated data storage libraries is resident on data storage media that is contained within a data storage cartridge, also referred to herein as a cartridge. An example of a data storage cartridge that is widely employed in automated data storage libraries for mass data storage is a magnetic tape cartridge.
In addition to data storage media, automated data storage libraries typically contain one or more data storage drives that store (write) data to and/or retrieve (read) data from the data storage media. Transport of cartridges between storage cells and storage drives is typically accomplished by one or more robot accessors. Such accessors have grippers for physically retrieving a selected cartridge from a storage cell within the automated data storage library and transporting the cartridge to a storage drive by moving in the horizontal (X) and/or vertical (Y) directions. Additionally, many libraries now include data drives of different types and the libraries must accommodate multiple types of cartridges to be used in the different drives.
Customer demands for storage have increased. One method for satisfying such demands has been the development of increased storage media density, along with new data drives, such that more data can be stored in the same amount of customer floor space. While increased media density has helped alleviate the forgoing demand, the need for increased storage has continued. While storage cells have traditionally been designed to hold a single data cartridge, a more recent development has been storage cells designed to be deep enough to hold two or even more data cartridges. Thus, with only an incremental increase in the library footprint, the data density of a library may be increased by a factor of two or more.
When a cell is deep enough for a single cartridge, the cartridge is always within reach of the accessor gripper. However, when a cell holds more than one cartridge and the front cartridge has been removed, it is necessary for the remaining cartridges to be moved forward to be reachable by the gripper. This can be accomplished by the use of a spring located in the rear of the cell which pushes the cartridges forward or by the use of an external mechanism which can reach into the cell and push the cartridges forward.
In a multi-cartridge cell, it requires extra time to remove a desired cartridge which is not at the front of the cell. Intermediate cartridges must first be removed and placed at a temporary location before the desired cartridge may be brought to the front of the cell and removed. The other cartridges must then be brought back to the cell and inserted. Such actions slow the overall access time to data stored on the cartridge.
Consequently, a need remains for more efficient management of data cartridges in an automated storage library having multiple-cartridge cells.